The new minister will take over from Seiji Maehara, pro-US security hawk, who quit on Sunday after admitting he had taken about $3,000 in donations from a Korean national.

"The prime minister made the decision based on his (Matsumoto's) abilities and knowledge, as well as on his diplomatic consistency - the fact that he has been involved in some important matters as state foreign secretary," Yukio Edano, chief cabinet secretary, told a news conference on Wednesday.

Matsumoto was first elected to parliament in 2000.

Key challenges

The appointment comes with a long list of challenges including managing strained ties with China and keeping ties with ally Washington on an even keel.

The resignation of Maehara, once seen as a likely successor to the unpopular Kan if he bows to pressure to quit, was a fresh blow to the premier and his Democratic Party of Japan (DPJ).

Kan is trying to pass bills needed to implement a $1 trillion budget for the year from April, through a gridlocked parliament, and craft policies to curb Japan's massive public debt.

The successor will have to hit the ground running, attending a G8 ministerial meeting in Paris on March 14-15 and a trilateral meeting with his counterparts from China and South Korea later this month.

Tsuneo Watanabe, a senior fellow at the Tokyo Foundation think tank, said that Matsumoto's policy views were pro-US and similar to Maehara's.

The two men share a "moderated engagement position" on China, "not hawkish, but not dovish", Watanabe said.

Delicate ties

Japan's relations with Beijing chilled markedly last year after Japan held a Chinese trawler captain following his boat's collision with Japanese patrol boats near disputed isles in the East China Sea.

In a sign that ties are still strained, Japan scrambled jets this month after Chinese naval planes flew near the isles, though they did not enter Japan's airspace.

Tokyo also complained to Beijing this week after a Chinese helicopter flew close to a Japanese destroyer in the East China Sea.

The relationship between Japan and Washington, Tokyo's biggest security ally, was also damaged after the DPJ took power in 2009 and Yukio Hatoyama, then-premier, tried to keep a campaign pledge to move a US airbase off the southern island of Okinawa.

Kan, who took over last June when Hatoyama suddenly quit, has promised to implement a 2006 deal to shift the base to a less populated part of the island, but faces stiff opposition from local residents.

Adding to the difficulties, Kevin Maher, the head of the Japan affairs office at the US state department, was recently quoted by Kyodo news agency as telling US college students that Okinawans were masters of "manipulation" and "extortion", sparking outrage in Okinawa.